This invention relates generally to motive fluids and more particularly to a motive fluid for an external combustion engine.
In designing and building an auxilliary power generating unit of the external combustion type, an important consideration was a suitable motive fluid. Such a unit is not designed for continuous operation and may be kept outdoors, hence the fluid should not freeze at expected winter temperatures. It must also be compatible with the materials with which it comes in contact. In the power unit built, ductile iron and carbon steel which are susceptible to corrosion if an acidic fluid is used, and aluminum which is attacked by highly alkaline fluids, were employed.
Additionally, the fluid should not readily decompose at the operating temperatures involved, should have as high a molecular weight as possible, should not be excessively dangerous and should be reasonably priced.
It should be noted that the prior art is replete with candidate working fluids, for example U.S. Pat. No. 3,516,248 includes pyridine and ethanol (see column 4, lines 2 and 6 respectively). In the research performed which led to this invention, however, it was found that such fluids would not satisfy the requirements given above.